In machining metallic work pieces, an apparatus called a tap is used to create internally threaded holes for receiving screws in the metallic work pieces. The tap itself is a tool with external cutting threads. In order to create the internally threaded hole in the work piece, the tap is rotated and driven into the work piece to the desired hole depth, and then reverse rotated and retracted from the work piece. The tap is generally held by a tap driver, and the tap driver is held or secured within a machine which provides the forward and reverse rotation as well as the forward and reverse drive.
In creating the internally threaded hole, the tap driver is first rotated and driven into the base material or metal to the desired depth. Once the tap reaches the desired depth, the rotation of the tap driver and the tap is reversed and the tap is retracted from the base material. In order to create the best internally threaded hole, the tap should be simultaneously advanced and rotated at precisely correlated rates of rotation and forward movement for a given tap pitch. By way of example, a one-quarter-twenty tap should be advanced into the work piece one inch for every twenty revolutions, or 0.05 inch for each revolution. In typical rigid tapping, the driver machines provide the synchronization of the spindle rotation and feed advance to match the tap pitch.
During the creation of a tap hole, the machine spindle goes through several stages, namely driving the rotating tap into the tap hole, slowing the forward drive or feed rate and the rotation until the tap comes to a stop in the work piece, reversing the direction of the rotation and accelerating or increasing the reverse rate of rotation to match the desired tap pitch as the tap is retracted. It will be appreciated by those of ordinary skill in the art that during the changes in rotation speed, the feed advance of the tap must be adjusted or correlated to precisely match the tap pitch. However, in practice it is very difficult to precisely match the rotation, drive and tap pitch and there are small errors that occur in the synchronization of the rotation speed and the feed rate during the deceleration or slowing down phase, and during the reverse rotation acceleration phase.
For many decades and back to the early 1900's, tension/compression tap drivers were used in production applications such as on transfer or assembly lines in the tapping or cutting of internally threaded holes in parts. These prior tension/compression devices required what the industry views as substantial movability in the tapping attachments because the tapping attachments would generally be utilized for multiple tap sizes and varying hole positions on different and irregular work surfaces. The old conventional machines and even the prior computer controlled machines utilized before rigid tapping was developed in the 1980's, required the springy tension/compression tapping attachments in order to produce good threads.
Around 1982, synchronous feed or rigid tap and control was invented and developed, and by approximately 1992 the computer programmed and CNC machines became widely used in industry, including for tapping. The precision and accuracy of the newly developed CNC machines changed the tapping industry by providing much more precise control over the entire tapping process and tool movement than the older tension/compression tapping attachments. It provided an improved way of tapping compared to the older tension/compression tapping attachments. The new CNC machines provided more precise movement of the tapping attachments and tools to the desired locations, more precise controls over the speed and rotation of the tapping attachments and tapping tools, and the changing of tapping tools utilized.
The industry soon recognized that the new use of rigid or synchronous tapping via CNC machines outperformed the older methods in several ways. For example, the speed at which the tapping occurred could be optimized for the particular tap, tap size and material being cut, versus the old method and tools wherein the tension/compression tapping attachments needed to be used because generally one slow speed was used for all taps in a multi-spindle tapping application. In another example, the new CNC machines provide a more accurate depth control, which can be important in tapping.
Due to the sophistication and precise performance capabilities of the newer CNC machines, the industry originally assumed that all that was required in the way of a tapping attachment was a simple rigid or soled tapping attachment or tap holder, and the CNC machines would do the rest. In fact, early in the process the machine builders recommended that solid rigid tap holders be used. Eventually rigid tapping has become the preferred and predominant way of cutting or tapping internally threaded holes.
Eventually some companies began to recognize the need to soften up the rigid tapping attachments while still maintaining the rigidness required by these applications. The industry knew the old tension/compression tapping attachments would not work in the new CNC applications and therefore began to use and develop plastic dampeners and O-rings to slightly soften the rigid tapping while still maintaining the rigidness required for rigid body tapping.
In machining numerous internally threaded apertures, one machine may be used to drill pilot holes into which the taps are driven, while a different machine may be used for the actual tapping. This may lead to slight positioning errors wherein the tap for instance is not exactly aligned with the pilot hole, but instead may be one or two thousandths of an inch off.
Some tapping attachments utilize a threaded adjusting screw to position the tap within the tapping attachment, and this adjusting screw allows the vertical adjustment of the tap relative to the tapping attachment. It has also been found that when the collet is tightened to secure the tap, it tends to want to draw the tap back up into the tapping attachment, which in turn can cause damage to the adjusting screw which has heretofor typically been fixed within the tapping attachment. It is an object of some embodiments of this invention to provide internal compressibility within the tapping attachment so that when the collet is tightened damage is minimized or avoided.
It will be appreciated by those of ordinary skill in the art that there is a need for a tap driver which has some limited flexure in the body of the tap driver for the location errors associated with locating the tap with respect to the desired tap hole location.
To achieve the precision and consistency of the flexure, it will also be appreciated by those of ordinary skill in the art that parts and materials for those components which can form an integrated part of the central body portion of the tap driver body can be very expensive. It is therefore an object of this invention to provide a tap driver system which minimizes the material needed for the flexure component to maintain a precise defined flexure.
Such a system as designed in some embodiments of the invention has an advantage of allowing the flexure component to be utilized in more than one type of tap driver if desired (for ease of manufacture and replacement, among other reasons). It is therefore another object of some embodiments of this invention to provide a universal central body portion or configuration which may be utilized in a plurality of different tap driver types, such as in a high pressure internal coolant, a cylindrical shank version, and/or a minimum quantity lubrication, to name a few.
It is also an object of some embodiments of this invention to provide a system to more easily interchange or replace flexure components within the tapping attachment. Some embodiments of this invention include a retaining ring which may be snapped into place around part or all of the flexure to fix it in its location within the tapping attachment. In these embodiments this would result in the flexure component, although it is of a different material, being integral with the other components of the tap driver body portion.
Other objects, features, and advantages of this invention will appear from the specification, claims, and accompanying drawings which form a part hereof. In carrying out the objects of this invention, it is to be understood that its essential features are susceptible to change in design and structural arrangement, with only one practical and preferred embodiment being illustrated in the accompanying drawings, as required.